A method for preparing high-toughness silicon carbide ceramic rods by pressureless sintering

Abstract

This invention provides a method for preparing high-toughness silicon carbide ceramic rods by pressureless sintering, belonging to the field of silicon carbide ceramics. The preparation method includes preparing silicon carbide nanowire-zirconia composites, preparing dispersed silicon carbide nanopowders, preparing ceramic powders, and molding and sintering. The preparation of silicon carbide nanowire-zirconia composites includes preparing zirconium sol, specifically by adding ZrOCl2·8H2O and La(NO3)3·6H2O to anhydrous ethanol, stirring evenly, adding tartaric acid solution, stirring at 40-42℃, adding kH560 silane coupling agent solution, stirring at 60-63℃ for 1.8-2.2h, adjusting the pH to 3.2-3.5, aging, adding polyacrylic acid, and stirring at 40-42℃ for 0.8-1.2h to obtain zirconium sol. The ceramic rods prepared by the method of this invention have improved toughness while enhancing strength, and also exhibit excellent high-temperature resistance and thermal shock resistance.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide ceramics, specifically relating to a method for preparing high-toughness silicon carbide ceramic rods by pressureless sintering. Background Technology

[0002] Silicon carbide ceramic rollers are columnar ceramic products made primarily from silicon carbide through specific molding and sintering processes. They are mainly used for material support, transport, and guidance under high temperature, corrosive, and load conditions. Silicon carbide ceramic rollers possess excellent high-temperature strength, good thermal stability, outstanding oxidation resistance and thermal shock resistance, as well as good wear resistance, making them indispensable key components in the industrial field and widely used in construction, glass, metallurgy, semiconductors, and other fields.

[0003] With the upgrading of high-end manufacturing industries, the performance requirements for silicon carbide ceramic rods are becoming increasingly stringent, with extreme requirements placed on their strength and high-temperature strength. The improvement of their performance directly promotes the technological progress and product quality upgrade of related downstream industries, and has significant economic and industrial value.

[0004] Existing technologies for improving the strength and high-temperature strength of silicon carbide ceramic rods typically involve refining the grains, using nanoscale silicon carbide particles, and optimizing sintering aids to achieve densification and extremely fine grain size, thereby improving the strength and hardness of the ceramic products.

[0005] However, when nanoparticles refine the grain size, their high specific surface area can easily lead to abnormal grain growth during sintering, which reduces density and strength. Furthermore, the fine grain structure results in a straight crack propagation path, making it difficult to activate toughening mechanisms such as crack deflection, thus making ceramic products prone to brittle fracture and significantly reducing fracture toughness. In addition, excessively fine grains and too many grain boundaries make it easy for microcracks to appear under extreme thermal cycling conditions, thereby shortening the product's service life.

[0006] Other methods involve introducing high-strength second-phase particles, such as titanium boride, to improve the product's strength and high-temperature strength. However, the thermal expansion coefficients of the second-phase particles and the silicon carbide matrix do not match, easily leading to stress concentration at the interface, and the stress cannot be effectively relieved, thus causing cracks. At the same time, the addition of second-phase particles hinders sintering densification, thereby affecting the improvement of strength and greatly reducing toughness. The interfacial compatibility between the second-phase particles and the silicon carbide matrix is ​​poor at high temperatures, and the bonding force at the interface is weak, resulting in a significant decrease in strength at high temperatures.

[0007] It is evident that while existing technologies improve the strength of silicon carbide ceramic rods at room temperature, they reduce the toughness and thermal shock resistance of ceramic products, and also result in lower high-temperature strength. This affects the use of silicon carbide ceramic rods in complex environments and shortens the product's service life. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention provides a method for preparing high-toughness silicon carbide ceramic rods by pressureless sintering, which improves the strength performance at room temperature while ensuring toughness, increasing high-temperature strength, and enhancing thermal shock resistance.

[0009] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0010] A method for preparing pressureless sintered high-toughness silicon carbide ceramic rods includes the following steps: preparing silicon carbide nanowire-zirconia composite, preparing dispersed silicon carbide nanopowder, preparing ceramic powder, and forming and sintering. The specific operations are as follows:

[0011] 1. Preparation of silicon carbide nanowire-zirconia composite

[0012] (1) Pretreatment of silicon carbide nanowires

[0013] Silicon carbide nanowires were placed in a 62-66 wt% concentrated nitric acid solution, and the temperature was raised to 78-82℃. The mixture was refluxed for 2.5-3.0 h. After reflux, the nanowires were removed, washed, and dried to obtain acid-impregnated silicon carbide nanowires. 28-32 g of acid-impregnated silicon carbide nanowires were uniformly placed in a CVD furnace. After removing the air, the temperature was raised to 940-960℃ at a rate of 4.5-5.0℃ / min under an argon atmosphere. Boron trichloride and ammonia were used as the reaction gas sources. The flow rate of boron trichloride was 14-16 mL / min, and the flow rate of ammonia was 42-48 mL / min. Argon was used as the carrier gas and dilution gas with a flow rate of 78-83 mL / min. The pressure was adjusted to 4.8-5.0 kPa, and the deposition time was 60-65 min to obtain pretreated silicon carbide nanowires.

[0014] The silicon carbide nanowires have a diameter of 45-55 nm and a length of 5.8-6.2 μm.

[0015] The mass ratio of the concentrated nitric acid solution to the silicon carbide nanowires is 6-8:1;

[0016] (2) Preparation of zirconium sol

[0017] Add ZrOCl2·8H2O and La(NO3)3·6H2O to anhydrous ethanol, stir at 180-210 rpm for 28-32 min, add tartaric acid solution, increase the temperature to 40-42℃ at a rate of 0.4-0.6℃ / min, keep warm and stir for 1.0-1.2 h, then add kH560 silane coupling agent solution, continue to increase the temperature to 60-63℃, keep warm and stir for 1.8-2.2 h, adjust the pH to 3.2-3.5, age at 50-53℃ for 20-24 h, add polyacrylic acid, stir at 40-42℃ for 0.8-1.2 h, and cool naturally to room temperature to obtain zirconium sol;

[0018] The mass ratio of anhydrous ethanol, ZrOCl2·8H2O, La(NO3)3·6H2O, tartaric acid solution, kH560 silane coupling agent solution, and polyacrylic acid is 100:32-35:1.0-1.5:34-37:2.3-2.6:0.4-0.6.

[0019] The tartaric acid solution is a mixture of deionized water and tartaric acid, wherein the mass ratio of deionized water to tartaric acid is 30:4-7.

[0020] The kH560 silane coupling agent solution is a mixture of kH560 silane coupling agent and deionized water, wherein the mass ratio of kH560 silane coupling agent to deionized water is 0.3-0.6:2.0.

[0021] (3) Composite

[0022] Pretreated silicon carbide nanowires were added to zirconium sol and ultrasonically dispersed for 38-43 min at a power of 220-240 W and a frequency of 28-33 kHz. After ultrasonic dispersion, the mixture was stirred at 70-74 °C for 1.8-2.2 h and dried. The temperature was then increased to 600-620 °C at a rate of 2.0-2.5 °C / min and held for 1.8-2.0 h. The temperature was then increased to 920-930 °C at a rate of 1.0-1.5 °C / min and held for 2.0-2.2 h. The mixture was then allowed to cool naturally to room temperature to obtain the silicon carbide nanowire-zirconia composite.

[0023] The mass ratio of zirconium sol to pretreated silicon carbide nanowires is 60-70:14-17.

[0024] 2. Preparation of Dispersible Silicon Carbide Nanopowder

[0025] (1) Vinyl treatment

[0026] Silicon carbide nanoparticles were placed in 5-7 times their weight of an 18-23 wt% hydrogen peroxide solution and stirred under reflux at 90-93°C for 3.7-4.0 h. After cooling, they were washed and dried, placed in toluene, and vinyltrimethoxysilane was added. The temperature was raised to 62-67°C and stirred for 3.5-4.0 h. After centrifugation, washing, and drying, vinylsilane-treated silicon carbide nanoparticles were obtained.

[0027] The particle size of the silicon carbide nanopowder is 160-190 nm.

[0028] The mass ratio of silicon carbide nanoparticles, toluene, and vinyltrimethoxysilane is 12-16:100:1.2-1.6;

[0029] (2) Photoinitiation

[0030] Cysteine ​​hydrochloride was added to N,N-dimethylformamide and stirred at 200-210 rpm for 25-30 min. Benzophenone was added and stirred evenly. Then, vinylsilane was added to treat silicon carbide nanoparticles. The mixture was ultrasonically dispersed for 20-25 min at an ultrasonic power of 160-170 W and an ultrasonic frequency of 23-28 kHz. After ultrasonic dispersion, the mixture was irradiated with ultraviolet light at a wavelength of 360-365 nm for 1.8-2.2 h. After the reaction, the mixture was centrifuged, washed, and vacuum dried at 110-115 °C to obtain dispersed silicon carbide nanoparticles.

[0031] The mass ratio of N,N-dimethylformamide, cysteine ​​hydrochloride, benzophenone, and vinylsilane used to treat silicon carbide nanoparticles is 80:0.7-1.0:0.10-0.13:12-16.

[0032] 3. Preparation of ceramic powder

[0033] Add ammonium polyacrylate and glycerol to deionized water, stir until homogeneous, then add 12-16 wt% ammonia solution to adjust the pH to 9.5-10.0. Add dispersible silicon carbide nanoparticles and silicon carbide nanowire-zirconia composite, disperse at high speed of 8000-8500 rpm for 25-30 min, then add polyvinyl alcohol, titanium boride and yttrium oxide, stir until homogeneous, and place in a water bath at 50-52℃, stir at 180-220 rpm for 1.8-2.2 h, and then spray granulate to obtain ceramic powder.

[0034] The mass ratio of deionized water, ammonium polyacrylate, glycerol, dispersible silicon carbide nanopowder, silicon carbide nanowire-zirconia composite, polyvinyl alcohol, titanium boride, and yttrium oxide is 200:0.8-1.2:0.4-0.6:28-32:4.4-4.6:3.4-3.6:0.8-1.2:0.8-1.2.

[0035] 4. Molding and sintering

[0036] The ceramic powder is placed into a mold and shaped to obtain a rough blank. The rough blank is heated to 620-650℃ in air at a rate of 1.8-2.0℃ / min and held for 1.5-2.0h. Then, in argon atmosphere, the temperature is increased to 1840-1860℃ at a rate of 3.5-4.0℃ / min and held for sintering for 2.2-2.5h. After naturally cooling to room temperature, silicon carbide ceramic rods are obtained.

[0037] This invention employs a pressureless sintering method to prepare silicon carbide ceramic rods, using silicon carbide nanopowder as the matrix and silicon carbide nanowires as the toughening phase. Specifically, boron nitride is first deposited on the surface of the silicon carbide nanowires. Boron nitride can alleviate the thermal mismatch stress between the silicon carbide nanowires and the matrix, effectively regulate stress transmission, and improve the interfacial bonding. Then, zirconium oxychloride is used as the zirconium source, lanthanum nitrate as the dopant phase, and tartaric acid as the complexing agent to form a zirconium oxide sol via a sol-gel method. Furthermore, kH560 silane coupling agent is introduced, whose epoxy groups can form chemical bonds with the zirconium sol, and the other end can bind to the silicon carbide nanowires, thereby enhancing the bonding force between the silicon carbide nanowires and the zirconium sol. In the composite step, the silicon carbide nanowires are uniformly dispersed in the zirconium sol, thus fully utilizing the toughening properties of the silicon carbide nanowires. The combination with zirconium oxide particles can prevent crack propagation.

[0038] In the preparation of dispersible silicon carbide nanopowder, hydrogen peroxide is first used to activate the silicon carbide nanopowder to provide more reaction sites. Then, it is treated with a vinyl silane coupling agent, which reacts with the hydroxyl groups on the surface of the silicon carbide nanopowder to impart vinyl groups to its surface. Then, cysteine ​​hydrochloride is introduced. Its thiol group can undergo a click chemical reaction with the vinyl group under the action of a photoinitiator and after ultraviolet light irradiation, thereby introducing amino groups on the silicon carbide nanopowder, which greatly improves the homogeneity and dispersibility of the ceramic powder.

[0039] In the ceramic powder preparation step, ammonium polyacrylate is used as a dispersant, polyvinyl alcohol as a binder, and titanium boride and yttrium oxide as sintering aids, which can further improve density and strength properties. Furthermore, the dispersible silicon carbide nanoparticles and silicon carbide nanowire-zirconia composites are combined to improve the compatibility of silicon carbide nanowires in the matrix, thereby enhancing toughness while improving strength, reducing thermal stress during thermal cycling, enhancing high-temperature strength and thermal shock resistance, and effectively extending the service life of silicon carbide ceramic rods.

[0040] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0041] 1. The silicon carbide ceramic rod prepared by the method of the present invention has a fracture toughness of 10.85-11.67 MPa·m. 1 / 2 The bending strength is 620.1-624.8 MPa, and the tensile strength is 278.6-284.2 MPa;

[0042] 2. The silicon carbide ceramic rod prepared by the method of the present invention was heated to 1500°C at a rate of 50°C / min in air, and held at that temperature for 120 hours. The fracture toughness was then measured again to be 10.42-11.41 MPa·m. 1 / 2 The bending strength is 596.5-606.7 MPa;

[0043] 3. The silicon carbide ceramic rods prepared by the method of the present invention were heated to 1200°C at a rate of 30°C / min in air, held at that temperature for 12 hours, and then immediately immersed in deionized water at 20°C for 12 hours. After immersion, they were dried at 110°C to constant weight. This process constitutes one thermal shock cycle. After 10 consecutive thermal shock cycles, the fracture toughness was measured again to be 10.21-11.10 MPa·m. 1 / 2 The bending strength is 576.7-588.6 MPa. Detailed Implementation

[0044] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0045] Example 1

[0046] 1. Preparation of silicon carbide nanowire-zirconia composite

[0047] (1) Pretreatment of silicon carbide nanowires

[0048] Silicon carbide nanowires were placed in a 64wt% concentrated nitric acid solution (7 times their weight), and the temperature was raised to 80℃. The mixture was refluxed for 2.7 h. After reflux, the nanowires were removed, washed, and dried to obtain acid-impregnated silicon carbide nanowires. 302 g of acid-impregnated silicon carbide nanowires were uniformly placed into a CVD furnace. After removing the air, the temperature was raised to 950℃ at a rate of 4.7℃ / min under an argon atmosphere. Boron trichloride and ammonia were used as the reaction gas sources, with a flow rate of 15 mL / min for boron trichloride and 45 mL / min for ammonia. Argon was used as the carrier gas and dilution gas, with a flow rate of 80 mL / min. The pressure was adjusted to 5.0 kPa, and the deposition time was 62 min to obtain pretreated silicon carbide nanowires.

[0049] The silicon carbide nanowires have a diameter of 450 nm and a length of 6.0 μm.

[0050] (2) Preparation of zirconium sol

[0051] Add 34g ZrOCl2·8H2O and 1.2g La(NO3)3·6H2O to 100g anhydrous ethanol, stir at 200rpm for 30min, add 36g tartaric acid solution, increase the temperature to 42℃ at a rate of 0.5℃ / min, keep warm and stir for 1.2h, then add 2.5g kH560 silane coupling agent solution, continue to increase the temperature to 62℃, keep warm and stir for 2.0h, adjust the pH to 3.4, age at 52℃ for 22h, add 0.5g polyacrylic acid, stir at 42℃ for 1.0h, and cool naturally to room temperature to obtain zirconium sol;

[0052] The tartaric acid solution is a mixture of deionized water and tartaric acid, wherein the mass ratio of deionized water to tartaric acid is 30:5.

[0053] The kH560 silane coupling agent solution is a mixture of kH560 silane coupling agent and deionized water, wherein the mass ratio of kH560 silane coupling agent to deionized water is 0.5:2.0.

[0054] (3) Composite

[0055] 15g of pretreated silicon carbide nanowires were added to 65g of zirconium sol and ultrasonically dispersed for 40min at a power of 230W and a frequency of 30kHz. After ultrasonic dispersion, the mixture was stirred at 72℃ for 2.0h. After drying, the temperature was increased to 610℃ at a rate of 2.3℃ / min and held for 2.0h. Then, the temperature was increased to 925℃ at a rate of 1.3℃ / min and held for 2.1h. The mixture was then allowed to cool naturally to room temperature to obtain the silicon carbide nanowire-zirconia composite.

[0056] 2. Preparation of Dispersible Silicon Carbide Nanopowder

[0057] (1) Vinyl treatment

[0058] 14g of silicon carbide nanoparticles were placed in 6 times their weight of a 20wt% hydrogen peroxide solution, stirred and refluxed at 92℃ for 3.8h, cooled, washed and dried, and then placed in 100g of toluene. 1.4g of vinyltrimethoxysilane was added, the temperature was raised to 65℃, and stirred for 3.8h. After centrifugation, washing and drying, vinylsilane-treated silicon carbide nanoparticles were obtained.

[0059] The silicon carbide powder has a particle size of 180 nm.

[0060] (2) Photoinitiation

[0061] Add 0.8g of cysteine ​​hydrochloride to 80g of N,N-dimethylformamide, stir at 205rpm for 28min, add 0.12g of benzophenone, stir evenly, then add 14g of vinylsilane to treat silicon carbide nanoparticles, and ultrasonically disperse for 23min at an ultrasonic power of 165W and an ultrasonic frequency of 25kHz. After ultrasonic dispersion, irradiate with ultraviolet light at a wavelength of 365nm for 2.0h. After the reaction, centrifuge, wash, and vacuum dry at 113℃ to obtain dispersed silicon carbide nanoparticles.

[0062] 3. Preparation of ceramic powder

[0063] Add 1.0g of ammonium polyacrylate and 0.5g of glycerol to 200g of deionized water, stir well, then add 14wt% ammonia solution to adjust the pH to 9.8, add 30g of dispersible silicon carbide nanoparticles and 4.5g of silicon carbide nanowire-zirconia composite, disperse at 8200rpm for 27min, then add 3.5g of polyvinyl alcohol, 1.0g of titanium boride and 1.0g of yttrium oxide, stir well, and place in a 52℃ water bath for 2.0h at 220rpm. After spray granulation, obtain ceramic powder.

[0064] 4. Molding and sintering

[0065] The ceramic powder is placed into a mold and shaped to obtain a rough blank. The rough blank is heated to 630°C at a rate of 2.0°C / min in air and held for 1.8h. Then, it is heated to 1850°C at a rate of 3.8°C / min in argon atmosphere and held for sintering for 2.3h. After naturally cooling to room temperature, silicon carbide ceramic rods are obtained.

[0066] Example 2

[0067] 1. Preparation of silicon carbide nanowire-zirconia composite

[0068] (1) Pretreatment of silicon carbide nanowires

[0069] Silicon carbide nanowires were placed in 8 times their mass of a 66wt% concentrated nitric acid solution, the temperature was raised to 82℃, and the reaction was refluxed for 3.0 h. After reflux, the nanowires were removed, washed, and dried to obtain acid-impregnated silicon carbide nanowires. 32 g of acid-impregnated silicon carbide nanowires were uniformly placed into a CVD furnace. After removing the air, the temperature was raised to 960℃ at a rate of 5.0℃ / min under an argon atmosphere. Boron trichloride and ammonia were used as the reaction gas sources, with a flow rate of 16 mL / min for boron trichloride and 48 mL / min for ammonia. Argon was used as the carrier gas and dilution gas with a flow rate of 83 mL / min. The pressure was adjusted to 5.0 kPa, and the deposition time was 65 min to obtain pretreated silicon carbide nanowires.

[0070] The silicon carbide nanowires have a diameter of 55 nm and a length of 6.2 μm.

[0071] (2) Preparation of zirconium sol

[0072] Add 35g ZrOCl2·8H2O and 1.5g La(NO3)3·6H2O to 100g anhydrous ethanol, stir at 210rpm for 32min, add 37g tartaric acid solution, raise the temperature to -42℃ at a rate of 0.6℃ / min, keep warm and stir for 1.2h, then add 2.6g kH560 silane coupling agent solution, continue to raise the temperature to 63℃, keep warm and stir for 2.2h, adjust the pH to 3.5, age at 53℃ for 24h, add 0.6g polyacrylic acid, stir at 42℃ for 1.2h, and cool naturally to room temperature to obtain zirconium sol;

[0073] The tartaric acid solution is a mixture of deionized water and tartaric acid, wherein the mass ratio of deionized water to tartaric acid is 30:7.

[0074] The kH560 silane coupling agent solution is a mixture of kH560 silane coupling agent and deionized water, wherein the mass ratio of kH560 silane coupling agent to deionized water is 0.6:2.0.

[0075] (3) Composite

[0076] 17g of pretreated silicon carbide nanowires were added to 70g of zirconium sol and ultrasonically dispersed for 43min at a power of 240W and a frequency of 33kHz. After ultrasonic dispersion, the mixture was stirred at 74℃ for 2.2h and dried. The temperature was then increased to 620℃ at a rate of 2.5℃ / min and held for 2.0h. The temperature was then increased to 930℃ at a rate of 1.5℃ / min and held for 2.2h. The mixture was then allowed to cool naturally to room temperature to obtain the silicon carbide nanowire-zirconia composite.

[0077] 2. Preparation of Dispersible Silicon Carbide Nanopowder

[0078] (1) Vinyl treatment

[0079] 16g of silicon carbide nanoparticles were placed in 7 times their weight of 23wt% hydrogen peroxide solution, stirred and refluxed at 93℃ for 4.0h, cooled, washed and dried, and placed in 100g of toluene. 1.6g of vinyltrimethoxysilane was added, the temperature was raised to 67℃, and stirred for 4.0h. After centrifugation, washing and drying, vinylsilane-treated silicon carbide nanoparticles were obtained.

[0080] The particle size of the silicon carbide powder is 190 nm;

[0081] (2) Photoinitiation

[0082] Add 1.0 g of cysteine ​​hydrochloride to 80 g of N,N-dimethylformamide, stir at 210 rpm for 30 min, add 0.13 g of benzophenone, stir evenly, add 16 g of vinylsilane to treat silicon carbide nanoparticles, and ultrasonically disperse for 25 min at an ultrasonic power of 170 W and an ultrasonic frequency of 28 kHz. After ultrasonic dispersion, irradiate with ultraviolet light at a wavelength of 365 nm for 2.2 h. After the reaction, centrifuge, wash, and vacuum dry at 115 °C to obtain dispersed silicon carbide nanoparticles.

[0083] 3. Preparation of ceramic powder

[0084] Add 1.2g of ammonium polyacrylate and 0.6g of glycerol to 200g of deionized water, stir well, then add 16wt% ammonia solution to adjust the pH to 10.0, add 32g of dispersible silicon carbide nanoparticles and 4.6g of silicon carbide nanowire-zirconia composite, disperse at 8500rpm for 30min, then add 3.6g of polyvinyl alcohol, 1.2g of titanium boride and 1.2g of yttrium oxide, stir well, and place in a 52℃ water bath for 2.2h at 220rpm. After spray granulation, obtain ceramic powder.

[0085] 4. Molding and sintering

[0086] The ceramic powder is placed into a mold and shaped to obtain a rough blank. The rough blank is heated to 650°C at a rate of 2.0°C / min in air and held for 2.0h. Then, it is heated to 1860°C at a rate of 4.0°C / min in argon atmosphere and held for 2.5h. After naturally cooling to room temperature, silicon carbide ceramic rods are obtained.

[0087] Example 3

[0088] 1. Preparation of silicon carbide nanowire-zirconia composite

[0089] (1) Pretreatment of silicon carbide nanowires

[0090] Silicon carbide nanowires were placed in a 62wt% concentrated nitric acid solution (6 times their weight), and the temperature was raised to 78℃. The mixture was refluxed for 2.5 h. After reflux, the nanowires were removed, washed, and dried to obtain acid-impregnated silicon carbide nanowires. 282 g of acid-impregnated silicon carbide nanowires were uniformly placed into a CVD furnace. After removing the air, the temperature was raised to 940℃ at a rate of 4.5℃ / min under an argon atmosphere. Boron trichloride and ammonia were used as the reaction gas sources, with a flow rate of 14 mL / min for boron trichloride and 42 mL / min for ammonia. Argon was used as the carrier gas and dilution gas, with a flow rate of 78 mL / min. The pressure was adjusted to 4.8 kPa, and the deposition time was 60 min to obtain pretreated silicon carbide nanowires.

[0091] The silicon carbide nanowires have a diameter of 45 nm and a length of 5.8 μm.

[0092] (2) Preparation of zirconium sol

[0093] Add 32g ZrOCl2·8H2O and 1.0g La(NO3)3·6H2O to 100g anhydrous ethanol, stir at 180rpm for 28min, add 34g tartaric acid solution, raise the temperature to 40℃ at a rate of 0.4℃ / min, keep warm and stir for 1.0h, then add 2.3g kH560 silane coupling agent solution, continue to raise the temperature to 60℃, keep warm and stir for 1.8h, adjust the pH to 3.2, age at 50℃ for 20h, add 0.46g polyacrylic acid, stir at 40℃ for 0.8h, and cool naturally to room temperature to obtain zirconium sol;

[0094] The tartaric acid solution is a mixture of deionized water and tartaric acid, wherein the mass ratio of deionized water to tartaric acid is 30:4.

[0095] The kH560 silane coupling agent solution is a mixture of kH560 silane coupling agent and deionized water, wherein the mass ratio of kH560 silane coupling agent to deionized water is 0.3:2.0.

[0096] (3) Composite

[0097] 14g of pretreated silicon carbide nanowires were added to 60g of zirconium sol and ultrasonically dispersed for 38min at a power of 220W and a frequency of 28kHz. After ultrasonic dispersion, the mixture was stirred at 70℃ for 1.8h. After drying, the temperature was increased to 600℃ at a rate of 2.0℃ / min and held for 1.8h. Then, the temperature was increased to 920℃ at a rate of 1.0℃ / min and held for 2.0h. The mixture was then allowed to cool naturally to room temperature to obtain the silicon carbide nanowire-zirconia composite.

[0098] 2. Preparation of Dispersible Silicon Carbide Nanopowder

[0099] (1) Vinyl treatment

[0100] 12g of silicon carbide nanoparticles were placed in 5 times their weight of 18wt% hydrogen peroxide solution, stirred and refluxed at 90℃ for 3.7h, cooled, washed and dried, and placed in 100g of toluene. 1.2g of vinyltrimethoxysilane was added, the temperature was raised to 62℃, and stirred for 3.5h. After centrifugation, washing and drying, vinylsilane-treated silicon carbide nanoparticles were obtained.

[0101] The silicon carbide powder has a particle size of 160 nm.

[0102] (2) Photoinitiation

[0103] Add 0.7g of cysteine ​​hydrochloride to 80g of N,N-dimethylformamide, stir at 200rpm for 25min, add 0.10g of benzophenone, stir evenly, add 12g of vinylsilane to treat silicon carbide nanoparticles, ultrasonically disperse for 20min at an ultrasonic power of 160W and an ultrasonic frequency of 23kHz. After ultrasonic dispersion, irradiate with ultraviolet light at a wavelength of 360nm for 1.8h. After the reaction, centrifuge, wash, and vacuum dry at 110℃ to obtain dispersed silicon carbide nanoparticles.

[0104] 3. Preparation of ceramic powder

[0105] Add 0.82g of ammonium polyacrylate and 0.4g of glycerol to 200g of deionized water, stir well, then add 12wt% ammonia solution to adjust the pH to 9.50, add 28g of dispersible silicon carbide nanoparticles and 4.4g of silicon carbide nanowire-zirconia composite, disperse at 8000rpm for 25min, then add 3.4g of polyvinyl alcohol, 0.8g of titanium boride and 0.8g of yttrium oxide, stir well, and place in a 50℃ water bath for 180rpm for 1.8h. After spray granulation, obtain ceramic powder.

[0106] 4. Molding and sintering

[0107] The ceramic powder is placed into a mold and shaped to obtain a rough blank. The rough blank is heated to 620°C at a rate of 1.8°C / min in air and held for 1.5h. Then, it is heated to 1840°C at a rate of 3.5°C / min in argon atmosphere and held for 2.2h. After naturally cooling to room temperature, silicon carbide ceramic rods are obtained.

[0108] Comparative Example 1-1

[0109] Based on Example 1, the following changes were made:

[0110] 1. Preparation of silicon carbide nanowire-zirconia composite

[0111] (1) Pretreatment of silicon carbide nanowires

[0112] The operation steps are exactly the same as in Example 1;

[0113] (2) Composite

[0114] 15g of pretreated silicon carbide nanowires and 8.4g of zirconium oxide powder were mixed and ultrasonically dispersed for 40min at an ultrasonic power of 230W and an ultrasonic frequency of 30kHz. After ultrasonic dispersion, the temperature was increased to 610℃ at a rate of 2.3℃ / min and held for 2.0h. Then the temperature was increased to 925℃ at a rate of 1.3℃ / min and held for 2.1h. The mixture was then allowed to cool naturally to room temperature to obtain the silicon carbide nanowire-zirconia composite.

[0115] The zirconium oxide powder has a particle size of 250 nm.

[0116] 2. Preparation of Dispersible Silicon Carbide Nanopowder

[0117] (1) Vinyl treatment

[0118] The operation steps are exactly the same as in Example 1, and the resulting vinylsilane-treated silicon carbide nanopowder is the dispersed silicon carbide nanopowder;

[0119] (2) The photoinitiation step is omitted.

[0120] 3. Preparation of ceramic powder

[0121] The operation steps are exactly the same as in Example 1.

[0122] 4. Molding and sintering

[0123] The operation steps are exactly the same as in Example 1.

[0124] Comparative Examples 1-2

[0125] 1. Preparation of silicon carbide nanowire-zirconia composite

[0126] (1) Omit the pretreatment steps for silicon carbide nanowires;

[0127] Silicon carbide nanowires were placed in a 62-66 wt% concentrated nitric acid solution (6-8 times their weight), the temperature was raised to 78-82℃, and the reaction was refluxed for 2.5-3.0 h. After reflux, the nanowires were removed, washed, and dried to obtain pretreated silicon carbide nanowires.

[0128] (2) Preparation of zirconium sol

[0129] The operation steps are exactly the same as in Example 1;

[0130] (3) Composite

[0131] The operation steps are exactly the same as in Example 1.

[0132] 2. Preparation of Dispersible Silicon Carbide Nanopowder

[0133] 12-16g of silicon carbide nanoparticles were placed in 5-7 times their weight of 18-23wt% hydrogen peroxide solution, stirred and refluxed at 90-93℃ for 3.7-4.0h, cooled, washed and dried, and then placed in 100g of toluene. 1.2-1.6g of kH550 silane coupling agent was added, the temperature was raised to 62-67℃, and stirred for 3.5-4.0h. After centrifugation, washing and drying, dispersible silicon carbide nanoparticles were obtained.

[0134] The particle size of the silicon carbide powder is 160-190 nm.

[0135] 3. Preparation of ceramic powder

[0136] The operation steps are exactly the same as in Example 1.

[0137] 4. Molding and sintering

[0138] The operation steps are exactly the same as in Example 1.

[0139] Performance testing

[0140] The silicon carbide ceramic rods prepared in Examples 1-3, Comparative Examples 1-1, and Comparative Examples 1-2 were subjected to the following performance tests:

[0141] 1. Performance at room temperature

[0142]

[0143] 2. High temperature resistance

[0144]

[0145] The high temperature resistance was tested by raising the temperature of the silicon carbide ceramic rods prepared in Examples 1-3, Comparative Examples 1-1, and Comparative Examples 1-2 to 1500°C in air at a rate of 50°C / min, holding them at that temperature for 120 hours, and then testing their fracture toughness and bending strength again.

[0146] 3. Thermal shock cycling resistance

[0147]

[0148] The thermal shock resistance test was conducted by heating silicon carbide ceramic rods prepared in Examples 1-3, Comparative Examples 1-1, and Comparative Examples 1-2 to 1200°C at a rate of 30°C / min in air, holding them at that temperature for 12 hours, and then immediately immersing them in deionized water at 20°C for 12 hours. After immersion, they were dried at 110°C to constant weight. This process was considered one thermal shock cycle. After 10 consecutive thermal shock cycles, the fracture toughness and bending strength were tested again.

[0149] Based on the above results, it can be seen that in Comparative Example 1-1, the pretreated silicon carbide nanowires were directly mixed with zirconium oxide powder using a mechanical mixing method. This resulted in poor dispersibility and strong agglomeration ability. Furthermore, the photoinitiation step was omitted in the preparation of dispersible silicon carbide nanopowder. The silicon carbide nanopowder treated with vinyl silane coupling agent had few active groups and poor dispersibility, which led to a large number of agglomerated particles in the ceramic powder. The interfacial bonding force between silicon carbide nanowires and silicon carbide powder was weak, resulting in low density after sintering. Moreover, the product could not effectively relieve stress and ultimately could not fully exert the toughening effect of silicon carbide nanowires, resulting in poor toughness, low strength, and poor stability of the product.

[0150] Comparative Examples 1-2 omitted the pretreatment of silicon carbide nanowires and directly composited them with zirconium sol, which reduced the compatibility and bonding force with zirconium sol, easily forming interfacial pores and weakening the reinforcing effect of silicon carbide nanowires. Furthermore, the direct treatment of silicon carbide powder with silane coupling agent to introduce amino groups on its surface resulted in the dispersibility of silicon carbide nanoparticles not reaching the effect of Example 1. This reduced the dispersibility and homogeneity of ceramic powder to a certain extent, ultimately causing the overall performance of the final product to fall short of the level of Example 1 and shortening its service life.

[0151] Unless otherwise specified, all proportions mentioned in this invention are mass proportions, and all percentages are mass percentages.

[0152] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a pressureless sintered high toughness silicon carbide ceramic rod, characterized by, The method comprises the steps of preparing a silicon carbide nanowire-zirconia composite, preparing a dispersible silicon carbide nanopowder, preparing a ceramic powder and forming and sintering. The step of preparing the silicon carbide nanowire-zirconia composite comprises the steps of silicon carbide nanowire pretreatment, zirconium sol preparation and compounding. The silicon carbide nanowire pretreatment step is as follows: the silicon carbide nanowires are put into a 62-66 wt% concentrated nitric acid solution, the temperature is raised to 78-82 ℃, and reflux reaction is carried out for 2.5-3.0 h; after the reflux is completed, the silicon carbide nanowires are taken out and dried; 28-32 g of the acid-impregnated silicon carbide nanowires are uniformly put into a CVD furnace, air is excluded, and the temperature is raised to 940-960 ℃ at a rate of 4.5-5.0 ℃ / min under an argon atmosphere; boron trichloride and ammonia are used as reaction gas sources, the flow rate of the boron trichloride is 14-16 mL / min, the flow rate of the ammonia is 42-48 mL / min, argon is used as a carrier gas and a dilution gas, the flow rate of the argon is 78-83 mL / min, the pressure is adjusted to 4.8-5.0 kPa, and the deposition time is 60-65 min, so as to obtain pretreated silicon carbide nanowires. The step of preparing the zirconium sol is as follows: ZrOCl2·8H2O and La(NO3)3·6H2O are added to anhydrous ethanol, a tartaric acid solution is uniformly stirred and added, stirring is carried out at 40-42 ℃ for 1.0-1.2 h, a kH560 silane coupling agent solution is added, stirring is carried out at 60-63 ℃ for 1.8-2.2 h, the pH value is adjusted to 3.2-3.5, and polyacrylic acid is added after aging, stirring is carried out at 40-42 ℃ for 0.8-1.2 h, so as to obtain the zirconium sol. The compounding step is as follows: the pretreated silicon carbide nanowires are added to the zirconium sol, ultrasonic dispersion is carried out, stirring is carried out at 70-74 ℃ for 1.8-2.2 h, the mixture is dried, the temperature is kept at 600-620 ℃ for 1.8-2.0 h, and the temperature is kept at 920-930 ℃ for 2.0-2.2 h, so as to obtain the silicon carbide nanowire-zirconia composite. The step of preparing the dispersible silicon carbide nanopowder comprises the steps of vinyl treatment and photo initiation. The step of vinyl treatment is as follows: the silicon carbide nanopowder is put into 5-7 times the mass of an 18-23 wt% hydrogen peroxide solution, stirring reflux is carried out at 90-93 ℃ for 3.7-4.0 h, the mixture is washed and dried after cooling, the mixture is put into toluene, vinyltrimethoxysilane is added, the temperature is raised to 62-67 ℃, and stirring is carried out for 3.5-4.0 h, so as to obtain the vinyl silane-treated silicon carbide nanopowder. The step of photo initiation is as follows: N,N-dimethylformamide is added with cysteamine hydrochloride and benzophenone, the mixture is uniformly stirred, the vinyl silane-treated silicon carbide nanopowder is added and ultrasonic dispersion is carried out for 20-25 min, and then ultraviolet light is used for irradiation reaction for 1.8-2.2 h, so as to obtain the dispersible silicon carbide nanopowder. The preparation of ceramic powder step is, to the deionized water is added ammonium polyacrylate and glycerin, after stirring uniform, add 12-16wt% ammonia solution to adjust pH to 9.5-10.0, add dispersible silicon carbide nano powder and silicon carbide nanowire-zirconia composite, 8000-8500rpm under high speed dispersion 25-30min, then add polyvinyl alcohol, titanium boride and yttrium oxide, after stirring uniform, put into to 50-52℃ water bath conditions, 180-220rpm stirring 1.8-2.2h, by spray granulation, obtain ceramic powder.

2. The preparation method of the high-toughness silicon carbide ceramic rod of claim 1, wherein, In the silicon carbide nanowire pretreatment step, the silicon carbide nanowire has a diameter of 45-55nm and a length of 5.8-6.2μm; The mass ratio of the concentrated nitric acid solution to the silicon carbide nanowire is 6-8:

1.

3. The preparation method of the high-toughness silicon carbide ceramic rod of claim 1, wherein, In the preparation of zirconium sol step, the mass ratio of the anhydrous ethanol, ZrOCl2·8H2O, La(NO3)3·6H2O, tartaric acid solution, kH560 silane coupling agent solution and polyacrylic acid is 100:32-35:1.0-1.5:34-37:2.3-2.6:0.4-0.6; The tartaric acid solution is a mixture of deionized water and tartaric acid, and the mass ratio of the deionized water to the tartaric acid is 30:4-7; The kH560 silane coupling agent solution is a mixture of kH560 silane coupling agent and deionized water, and the mass ratio of the kH560 silane coupling agent to the deionized water is 0.3-0.6:2.

0.

4. The preparation method of the high-toughness silicon carbide ceramic rod of claim 1, wherein, In the compounding step, the mass ratio of the zirconium sol to the pretreated silicon carbide nanowire is 60-70:14-17.

5. The preparation method of the high-toughness silicon carbide ceramic rod of claim 1, wherein, In the vinyl treatment step, the particle size of the silicon carbide nanometer powder is 160-190nm; The mass ratio of the silicon carbide nanometer powder, toluene and vinyl trimethoxysilane is 12-16:100:1.2-1.

6.

6. The preparation method of the high-toughness silicon carbide ceramic rod of claim 1, wherein, In the light initiation step, the mass ratio of N,N-dimethylformamide, cysteamine hydrochloride, benzophenone and vinyl silane treated silicon carbide nanometer powder is 80:0.7-1.0:0.10-0.13:12-16.

7. The preparation method of the high-toughness silicon carbide ceramic rod of claim 1, wherein, The mass ratio of the deionized water, ammonium polyacrylate, glycerol, dispersible silicon carbide nano-powder, silicon carbide nanowire-zirconia composite, polyvinyl alcohol, titanium boride, yttrium oxide in the step of preparing ceramic powder is 200:0.8-1.2:0.4-0.6:28-32:4.4-4.6:3.4-3.6:0.8-1.2:0.8-1.

2. 8.The method of claim 1, wherein the method further comprises: preparing the silicon carbide ceramic rod by the following steps: a forming and sintering step. The forming and sintering step is that the ceramic powder is put into a mold to obtain a rough blank, the rough blank is heated to 620-650 ℃ at a rate of 1.8-2.0 ℃ / min in air atmosphere, and then heated to 1840-1860 ℃ at a rate of 3.5-4.0 ℃ / min in argon atmosphere, and sintered for 2.2-2.5 h, and then naturally cooled to room temperature to obtain the silicon carbide ceramic rod.

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